Alloy for magnesium and magnesium alloy grain refinement and preparation method thereof

ABSTRACT

The present invention provides an alloy for magnesium and magnesium alloy grain refinement, and a preparation method thereof, the alloy as a grain refiner being an aluminum-zirconium-boron intermediate alloy comprising the following chemical compositions by weight percent: 5-20% of Zr, 0.5-4% of B, and the balance being Al. The invention can achieve the following technical effect: an intermediate alloy with strong nucleation capability and excellent capability of magnesium and magnesium alloy grain refinement is invented and its preparation method is provided. This kind of grain refiner can be applied to casting deformation plastic processing of magnesium and magnesium alloy profiles, with high degree of refinement, to promote the extensive industrial applications of magnesium.

FIELD OF THE INVENTION

The present invention relates to an intermediate alloy that improves the properties of metal and alloy, in particular, to a grain refiner of magnesium and magnesium alloy and its preparation method thereof.

BACKGROUND OF THE INVENTION

Magnesium and magnesium alloys are the lightest metal structural materials available now, which have such advantages as low density, high specific strength and specific stiffness, good damping resistance, good thermal conductivity, excellent electromagnetic shielding effect, excellent machining performance, stable part size and easy to recycle, etc.. Magnesium and magnesium alloys, especially wrought magnesium alloy have enormous application potential in transportation tools, engineering structure materials and electronics industries, etc.. Wrought magnesium alloys refer to those magnesium alloys that can be processed by plastic molding methods such as extrusion, rolling, forging, etc.. However, restricted by some factors such as preparation of materials, processing technology, corrosion resistance performance and price, the applications of magnesium alloy especially wrought magnesium alloy are far less than steel and aluminum alloys. There is a great gap between the development potential and actual applications of magnesium and magnesium alloy in the field of metal materials.

Zr is the element that has obvious refining effect of pure magnesium grains. Studies have shown that Zr can effectively inhibit the growth of magnesium alloy grains to refine the grains. Zr can be used in pure Mg, Mg—Zn and Mg-RE; but Zr has very low solubility in liquid magnesium, and when peritectic reaction occurs, only 0.6wt % Zr can be dissolved in liquid magnesium; moreover, Zr and Al, Mn will form a stable compound to precipitate, which cannot achieve the effect of grains refinement. Therefore, Zr cannot be added to Mg—Al-based and Mg—Mn-based alloys. Currently, Mg—Al-based alloy is the most popular commercial magnesium alloy. The Mg—Al-based alloy has a large as-cast grain, and sometime even shows large columnar crystals and fan-like crystals, which makes deformation of ingots, difficult in processing, easy to crack, low yield, poor mechanical properties, and very low plastic deformation rate, which seriously affects the industrial production. Therefore, in order to achieve large-scale production, it is necessary to resolve the problem of as-cast grain refinement of magnesium alloys. The grain refinement method of Mg—Al alloys mainly includes overheating method, rare earth element method and carbon inoculation method, etc.. Overheating method has some effect, but the melt oxidation is more serious, while the rare earth element method is neither stable nor ideal. The carbon inoculation method, due to its extensive sources of raw materials, low operating temperature, has become the most important grain refinement method of Mg—Al-based alloys. The traditional carbon inoculation method is to add MgCO₃ or C₂Cl₆ , etc.. Its principle is to form a large number of dispersed Al₄C₃ particles. Al₄C₃ is a better heterogeneous nucleation of magnesium alloy, thus, a large number of dispersed Al₄C₃ nuclei can make refinement of magnesium alloy grains. However, when such grain refiner is added, melt is easy to boil, so it is rarely used in the production. In short, as compared with the aluminum alloy industry, no common intermediate alloy of grain refinement is available in the magnesium alloy industry now, and the application range of various grain refinement methods also depends on the alloy-based or alloy compositions.

Thus, to invent a kind of common grain refiner (alloy) for effective refinement of as-cast grains during solidification of magnesium and magnesium alloys is one of the key factors to realize industrialization of wrought magnesium and its alloys.

SUMMARY OF THE INVENTION

In order to overcome the deficiencies of the prior arts, the present invention provides an intermediate alloy used for grain refinement of magnesium and magnesium alloy. This kind of intermediate alloy has very strong nucleation ability for magnesium and magnesium alloy. This invention also provides the preparation method of the intermediate alloy.

Numerous experimental studies of magnesium alloy grain refinement have shown that, ZrB₂ is a kind of crystal nucleus with nucleation ability several times stronger than Al₄C₃ The Al—Zr—B intermediate alloy prepared has very low melting point, which may form a large number of dispersed ZrB₂ and ZrAl₃ particles after melting in magnesium alloy to become better heterogeneous crystal nuclei of magnesium alloy.

The technical scheme adopted in this invention is as follows:

An alloy for magnesium and magnesium alloy grain refinement is provided, and the grain refiner being an aluminum-zirconium-boron intermediate alloy comprising the following chemical compositions by weight percent: 5-20% of Zr, 0.5-4% of B, and the balance being Al.

Preferably, the grain refiner is an aluminum-zirconium-boron intermediate alloy comprising the following chemical compositions by weight percent: 5.0±0.5% of Zr, 0.5±0.25% of B and the balance being Al.

Preferably, the grain refiner is an aluminum-zirconium-boron intermediate alloy comprising the following chemical compositions by weight percent: 5.0±0.5% of Zr, 1.0±0.25% of B and the balance being Al.

Preferably, the grain refiner is an aluminum-zirconium-boron intermediate alloy comprising the following chemical compositions by weight percent: 10.0±1.0% of Zr, 2.0±0.3% of B and the balance being Al.

Preferably, the grain refiner is an aluminum-zirconium-boron intermediate alloy comprising the following chemical compositions by weight percent: 15.0±2.0% of Zr, 3.0±0.5% of B and the balance being Al.

Preferably, the grain refiner is an aluminum-zirconium-boron intermediate alloy comprising the following chemical compositions by weight percent: 20.0±3.0% of Zr, 4.0±0.7% of B and the balance being Al.

Preferably, the impurities of said aluminum-zirconium-boron intermediate alloy comprise the following chemical compositions by weight percent: Fe0.5≦0.5% Si≦0.3%, Cu≦0.2%, Cr≦0.2% and other single impurity element≦0.2%.

This invention also provides a preparation method of alloy for magnesium and magnesium alloy grain refinement, comprising the following steps:

Step A: Add aluminum in a reactor, heat it to 700-850, and add the mixture of fluorozirconate and fluoroborate to the reactor;

Step B: After stirring 4-6 hours, extract the upper layer of molten liquid, to remain the lower layer of aluminum-zirconium-boron alloy;

Step C: After deslagging and heat preservation, the resulting aluminum-zirconium-boron alloy can be directly cast, particularly prepared into wire rod with diameter of 9.5 mm in a way of continuous casting and rolling or continuous casting and extrusion.

Wherein the aluminum is added excessively.

Preferably, the mole fraction f fluorozirconate to fluoroborate is 1:1 or 1:2.

Preferably, the fluorozirconate is potassium fluorozirconate , and the fluoroborate is potassium fluoroborate.

The equation of chemical reactions is as follow:

$\left. {{{Al}\mspace{14mu} ({excess})} + {x\mspace{14mu} K_{2}{ZrF}_{6}} + {y\mspace{14mu} {KBF}_{4}}}\rightarrow{{{{Al} \cdot {Zr} \cdot B}\mspace{14mu} ({alloy})} + {\frac{{3y} + {6x}}{{3y} + {4x}}{{KF} \cdot {AlF}_{3}}}} \right.$

Wherein the aluminum is added excessively.

Preferably, the fluorozirconate is sodium fluorozirconate , and the fluoroborate is sodium fluoroborate.

The equation of chemical reactions is as follow:

$\left. {{{Al}({excess})} + {x\mspace{14mu} {Na}_{2}{ZrF}_{6}} + {y\mspace{14mu} {NaBF}_{4}}}\rightarrow{{{{Al} \cdot {Zr} \cdot B}\mspace{14mu} ({alloy})} + {\frac{{3y} + {6x}}{{3y} + {4x}}{{{Na}F} \cdot {AlF}_{3}}}} \right.$

Wherein the aluminum is added excessively.

The invention can achieve the following technical effect: an intermediate alloy with strong nucleation capability and excellent capability of magnesium and magnesium alloy grain refinement is invented. This kind of grain refiner can be applied to casting and rolling of magnesium and magnesium alloy profiles, with high degree of refinement, to promote the extensive industrial applications of magnesium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the metallograph of aluminum-zirconium-boron alloy under 100 folds in Embodiment 1.

FIG. 2 shows the metallograph of aluminum-zirconium-boron alloy under 100 folds in Embodiment 3.

FIG. 3 shows the comparative photo of alloys before and after grain refinement prepared in Embodiment 1.

FIG. 4 shows the comparative photo of alloys before and after grain refinement prepared in Embodiment 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

Weigh 100 kg aluminum and put it in a reactor, heat it to 750, and add the mixture of 15.8 kg potassium fluozirconate and 11.58 kg potassium fluoborate to the reactor. After stirring 4 hours, extract the upper layer of molten liquid, to remain the lower layer of aluminum-zirconium-boron alloy of 94% Al-5% Zr-1% B. After deslagging and heat preservation, the resulting aluminum -zirconium-boron alloy can be directly rolled into wire rods with diameter of 9.5 mm in a way of continuous casting and rolling.

Embodiment 2

Weigh 100 kg aluminum and put it in a reactor, heat it to 700, and add the mixture of 14 kg sodium fluozirconate and 10.1 kg sodium fluoborate to the reactor. After stirring 6 hours, extract the upper layer of molten liquid, to remain the lower layer of aluminum-zirconium-boron alloy of 94% Al-5% Zr-1% B. After deslagging and heat preservation, the resulting aluminum-zirconium-boron alloy can be directly used by casting molding.

Embodiment 3

Weigh 100 kg aluminum and put it in a reactor, heat it to 800° C., and add the mixture of 32.23 kg potassium fluozirconate and 23.74 kg potassium fluoborate to the reactor. After stirring 6 hours, extract the upper layer of molten liquid, to remain the lower layer of aluminum-zirconium-boron alloy of 88% Al-10% Zr-2% B. After deslagging and heat preservation, the resulting aluminum-zirconium-boron alloy can be directly rolled into wire rods with diameter of 9.5 mm in a way of continuous casting and rolling.

Embodiment 4

Weigh 100 kg aluminum and put it in a reactor, heat it to 850° C., and add the mixture of 28.59 kg sodium fluozirconate and 20.73 kg sodium fluoborate to the reactor. After stirring 5 hours, extract the upper layer of molten liquid, to remain the lower layer of aluminum-zirconium-boron alloy of 88% Al-10% Zr-2% B. After deslagging and heat preservation, the resulting aluminum-zirconium-boron alloy can be directly used by casting molding.

As shown from FIG. 1, Al-5% Zr-1% B comprises two phases. Al₃Zr in the photo is gray flocculent or massive phase, dispersed in the metal; ZrB₂ is black particulate, with very small size, and most of which are of submicron order.

As shown from FIG. 2, compared with Al-5% Zr-1% B, in the Al-10% Zr-2% B, Al₃Zr is still gray flocculent or massive phase, and ZrB2 is black particulate, with increased size in both phases.

FIG. 3-a is the metallograph of pure magnesium and its grain is a 1-8 mm columnar crystal in width, in scattered distribution; FIGS. 3-b and 3-c are the metallographs of pure magnesium added with 2% and 5% Al-5% Zr-1% B respectively; as shown from these figures, the central parts are all equiaxed grains, surrounded by a small amount of columnar crystals, with the grain size of 300 μm-2 mm when the added amount is 2%, and with the grain size of 100 μm-1 mm when the added amount is 5%. FIG. 4-b and FIG. 4-c are the metallographs of pure magnesium added with 2% and 5% Al-10% Zr-2% B alloys. As shown from the figures, all grains are refined into equiaxed grains, with the grain size of 200 μm-1.5 mm when the added amount is 2%, and with the grain size of 100 μm-1 mm when the added amount is 5%. The test results show that Al—Zr—B intermediate alloy in the present invention has good effect of grain refinement for magnesium alloys.

The foregoing invention has been described in detail by way of illustration and example for purposes of clarity and understanding. As is readily apparent to one skilled in the art, the foregoing are only some of the methods and compositions that illustrate the embodiments of the foregoing invention. It will be apparent to those of ordinary skill in the art that variations, changes, modifications and alterations may be applied to the compositions and/or methods described herein without departing from the true spirit, concept and scope of the invention. 

1. An alloy for magnesium and magnesium alloy grain refinement, wherein the grain refiner is an aluminum-zirconium-boron intermediate alloy comprising the following chemical compositions by weight percent: 5-20% of Zr, 0.5-4% of B, and the balance being Al.
 2. The alloy for magnesium and magnesium alloy grain refinement according to claim 1, wherein the grain refiner is an aluminum-zirconium-boron intermediate alloy comprising the following chemical compositions by weight percent: 5.0±0.5% of Zr, 0.5±0.25% of B and the balance being Al.
 3. The alloy for magnesium and magnesium alloy grain refinement according to claim 1, wherein the grain refiner is an aluminum-zirconium-boron intermediate alloy comprising the following chemical compositions by weight percent: 5.0±0.5% of Zr, 1.0±0.25% of B and the balance being Al.
 4. The alloy for magnesium and magnesium alloy grain refinement according to claim 1, wherein the grain refiner is an aluminum-zirconium-boron intermediate alloy comprising the following chemical compositions by weight percent: 10.0±1.0% of Zr, 2.0±0.3% of B and the balance being Al.
 5. The alloy for magnesium and magnesium alloy grain refinement according to claim 1, wherein the grain refiner is an aluminum-zirconium-boron intermediate alloy comprising the following chemical compositions by weight percent: 15.0±2.0% of Zr, 3.0±0.5% of B and the balance being Al.
 6. The alloy for magnesium and magnesium alloy grain refinement according to claim 1, wherein the grain refiner is an aluminum-zirconium-boron intermediate alloy comprising the following chemical compositions by weight percent: 20.0±3.0% of Zr, 4.0±0.7% of B and the balance being Al.
 7. The alloy for magnesium and magnesium alloy grain refinement according to claim 1, wherein the impurities of said aluminum-zirconium-boron intermediate alloy comprise the following chemical compositions by weight percent: Fe≦0.5%, Si≦0.3%, Cu≦0.2%, Cr≦0.2% and other single impurity element≦0.2%.
 8. A preparation method of alloy for magnesium and magnesium alloy grain refinement according to claim 1, comprising the following steps: Step A: Add aluminum in a reactor, heat it to 700-850° C., and add the mixture of fluorozirconate and fluoroborate to the reactor; Step B: After stirring 4-6 hours, extract the upper layer of molten liquid, to remain the lower layer of aluminum-zirconium-boron alloy; Step C: After deslagging and heat preservation, the resulting aluminum-zirconium-boron alloy can be directly cast, particularly prepared into wire rod with diameter of 9.5 mm in a way of continuous casting and rolling or continuous casting and extrusion; wherein the aluminum is added excessively.
 9. The preparation method according to claim 8, wherein the mole fraction f fluorozirconate to fluoroborate is 1:2 to 1:1.
 10. The preparation method according to claim 8, wherein the fluorozirconate is potassium fluorozirconate or sodium fluorozirconate, and the fluoroborate is potassium fluoroborate or sodium fluoroborate.
 11. The preparation method according to claim 9, wherein the fluorozirconate is potassium fluorozirconate or sodium fluorozirconate, and the fluoroborate is potassium fluoroborate or sodium fluoroborate.
 12. A preparation method of alloy for magnesium and magnesium alloy grain refinement according to claim 2, comprising the following steps: Step A: Add aluminum in a reactor, heat it to 700-850° C., and add the mixture of fluorozirconate and fluoroborate to the reactor; Step B: After stirring 4-6 hours, extract the upper layer of molten liquid, to remain the lower layer of aluminum-zirconium-boron alloy; Step C: After deslagging and heat preservation, the resulting aluminum-zirconium-boron alloy can be directly cast, particularly prepared into wire rod with diameter of 9.5 mm in a way of continuous casting and rolling or continuous casting and extrusion; wherein the aluminum is added excessively.
 13. A preparation method of alloy for magnesium and magnesium alloy grain refinement according to claim 3, comprising the following steps: Step A: Add aluminum in a reactor, heat it to 700-850° C., and add the mixture of fluorozirconate and fluoroborate to the reactor; Step B: After stirring 4-6 hours, extract the upper layer of molten liquid, to remain the lower layer of aluminum-zirconium-boron alloy; Step C: After deslagging and heat preservation, the resulting aluminum-zirconium-boron alloy can be directly cast, particularly prepared into wire rod with diameter of 9.5 mm in a way of continuous casting and rolling or continuous casting and extrusion; wherein the aluminum is added excessively.
 14. A preparation method of alloy for magnesium and magnesium alloy grain refinement according to claim 4, comprising the following steps: Step A: Add aluminum in a reactor, heat it to 700-850° C., and add the mixture of fluorozirconate and fluoroborate to the reactor; Step B: After stirring 4-6 hours, extract the upper layer of molten liquid, to remain the lower layer of aluminum-zirconium-boron alloy; Step C: After deslagging and heat preservation, the resulting aluminum-zirconium-boron alloy can be directly cast, particularly prepared into wire rod with diameter of 9.5 mm in a way of continuous casting and rolling or continuous casting and extrusion; wherein the aluminum is added excessively.
 15. A preparation method of alloy for magnesium and magnesium alloy grain refinement according to claim 5, comprising the following steps: Step A: Add aluminum in a reactor, heat it to 700-850° C., and add the mixture of fluorozirconate and fluoroborate to the reactor; Step B: After stirring 4-6 hours, extract the upper layer of molten liquid, to remain the lower layer of aluminum-zirconium-boron alloy; Step C: After deslagging and heat preservation, the resulting aluminum-zirconium-boron alloy can be directly cast, particularly prepared into wire rod with diameter of 9.5 mm in a way of continuous casting and rolling or continuous casting and extrusion; wherein the aluminum is added excessively.
 16. A preparation method of alloy for magnesium and magnesium alloy grain refinement according to claim 6, comprising the following steps: Step A: Add aluminum in a reactor, heat it to 700-850° C., and add the mixture of fluorozirconate and fluoroborate to the reactor; Step B: After stirring 4-6 hours, extract the upper layer of molten liquid, to remain the lower layer of aluminum-zirconium-boron alloy; Step C: After deslagging and heat preservation, the resulting aluminum-zirconium-boron alloy can be directly cast, particularly prepared into wire rod with diameter of 9.5 mm in a way of continuous casting and rolling or continuous casting and extrusion; wherein the aluminum is added excessively.
 17. A preparation method of alloy for magnesium and magnesium alloy grain refinement according to claim 7, comprising the following steps: Step A: Add aluminum in a reactor, heat it to 700-850° C., and add the mixture of fluorozirconate and fluoroborate to the reactor; Step B: After stirring 4-6 hours, extract the upper layer of molten liquid, to remain the lower layer of aluminum-zirconium-boron alloy; Step C: After deslagging and heat preservation, the resulting aluminum-zirconium-boron alloy can be directly cast, particularly prepared into wire rod with diameter of 9.5 mm in a way of continuous casting and rolling or continuous casting and extrusion; wherein the aluminum is added excessively. 